Chapter 6 - Construction
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Chapter 6 - Construction Rods and Valve Gear Rods and Valve Gear Please download the Rods and Valve Gear PDF drawings NOW! These drawings do have some parts that you will need to cut from the PDF's, but most of these PDF's are about assembly of pre-made parts. So in a sense this chapter is easier than earlier ones, in that you don't actually have very much to make. That doesn't mean the installation of the pre-made parts will be easy. There are a lot of fine tolerances and clearance issues, which will keep you, occupied, and can at times be frustrating! The Mason Valve gear is a very complex piece of machinery, more so than most Walschaert's gear from later ages. It has a lot of moving parts. Be that as it may, you will finish up with an accurate fitment of a Mason valve gear, and everything will work per prototype. There are very few electric sized models in existence that have gone this far. Download the PDF's here 0-6-6T and 2-6-6T Valve Gear PDF's. <<2-6-6T-31.zip>> 2-8-6T Valve Gear PDF's. <<2-8-6T.zip>> Note that the 2-8-6T valve gear is a variant of the 2-6-6T version, and will require some additional rods to be hand made. The construction is not covered in detail in this chapter, but shown in the 2-8-6T PDF's. Most of the laser cut valve set can be used, however new crossheads, double crosshead guides and valve rod at the valve chest will need to be made. This is shown in the PDF. Additionally, there is no reason why you can't actually use the 2-6-6T valve gear on the 2-8-6T if you're prepared to wear the few differences in the design. Copyright 2002 - myLargescale.com/Model Railroads Online, LLC Page 1 Download these two Quicktime movies that show the finished Valve gear in motion. Please refer to these two films often while you install your valve gear so that you can get an idea of how things move. <<DSCN1063.MOV and DSCN1071.MOV>> From the outset I want you to keep the PDF entitled 'Rod Names' handy at all times. There are a whole bunch of rods and bits and pieces in this job and it's important we all call the parts by the same name. These are also generally the correct names for these parts. Mason however had some extra rods and cams up on the front end, which are not on any other Walschaert's gear in history, and thus I had to take a punt at the names of those parts. The PDF set also includes some nine information-only drawings showing how the real Mason pilot truck looked, the bar frame, the steam pipe connections, bogie pivot details and tender truck details. These are included only to satisfy your curiosity, as most of these details cannot be added to a working electric model running on tight curves! But for completeness, I thought you guys should know some more about how these Mason Bogies worked. A Little History First I know you're itching to get into installing this valve gear, but lets stop a moment and talk about what we're actually trying to replicate. As you know, William Mason was the first in the US to apply the Belgian 'Walschaert's Valve Gear' to a locomotive. You need to understand that the Walschaert's was more an 'idea' than a prescribed way to build a valve gear. The system would differ based on wheel size, valve travel, crank throw etc. Mason took the idea of the Walschaert's, and adapted it to be implemented on this W.M. Mason 0-6-6T in 1874: In very quick succession, Mason developed a number of versions to this valve gear. At first I thought this was a developmental process, however closer examination of the locomotives rolled out in order shows all the variants were used again and again. I realised Mason had developed and applied three different valve gear systems between 1874 and 1883. The three systems did have variants. The three systems, developed in this order were for: Larger Bogie Locos (such as W.M. Mason, Leviathan and many more). Smaller Bogie locos (such as the 1876 centennial Mason, and AA Denny) Mid-sized Bogie Locos (such as Bully Boy and the locos of the DSP&P) All three systems were essentially the same in principle, the differences relate to how Mason combined the eccentric movements and combination rods into one motion. Why he created and used 3 systems depending on loco size, I don't know. Maybe there were different advantages in the systems based on the length over the chassis and the amount of movement required in the valve chest. Copyright 2002 - myLargescale.com/Model Railroads Online, LLC Page 2 Fundamentally the Walschaert's system combines two basic rod movements to power the valve rod into the valve chest. The two rod movements are the Eccentric rod off the 3rd axle, and the Combination rods off the crosshead. Both move in different ways, and combined at the radius Rod get the desired valve movement controlling the admission of steam to the cylinders. All three of Mason's valve gear methods meet the above requirement, only in different ways. Larger Loco Valve Gear The system used on the larger locomotives was pretty simple. As seen in the W.M. Mason photo above, the eccentric rod comes off the third axle per normal. The combination rods come off the crosshead and swing to the rear of the crosshead (not in front like later years). The combination rods and eccentric rod meet the radius rod just behind the lead driver. From that position, the valve rod has a nice, long, straight run at the steam chests across the lead driver. This became almost a standard valve set up for larger 6-wheel bogies from the Mason works. However in late 1874, Mason built the first of his larger 6-wheel bogie narrow gauge locos - a loco to be named 'Tomales' for the North Pacific Coast RR. This smaller 0-6-6T loco was the first narrow gauge loco to be fitted with a Walschaert's valve gear in the US. Believed to be too heavy, she was regauged for a Texas road in 1875. The interesting thing about this first NG Walschaert's valve gear is that it was a one-off design, based on the W.M. Mason design, but with modifications that formed the basis of the 'smaller' valve gear used on Mason's typical 0-4-4T locos. Seen above the larger system as applied to Leviathan. Note the combination rods to the rear of the crosshead, and the radius rod hidden inside the link cradle. The valve rod runs clean across the top of the crossheads to the steam chest. The Original valve gear of this type applied to W.M. Mason in 1874. Copyright 2002 - myLargescale.com/Model Railroads Online, LLC Page 3 The Small Loco Valve Gear This was the second basic valve gear designed after the Tomales design, and a type used on the 1876 Centennial 0-4-4T Mason, along with most other smaller 0-4-4Ts using external valve gear. Because of the compact nature of the valve gear, and position of the combination rods so close to the valve chest, Mason created a long, wide sliding block (link block), with the combination rod/radius rod fitment to one side of the block, and the valve rod connected to the inside edge of the block. The whole block slides back and forth through a stanchion off the lead end of the crosshead guide, and a glide box fitted off the crosshead guide support at the rear end. The object was to transfer the outside motion of the valve gear to the inward position of the steam chest, without any losses of movement in the transfer. The outcome is that the radius rod's motion is transferred inboard to the steam chest location in a simple way. Why didn't he just do this on the mid-sized locos as well? Donno. Maybe the smaller locos had the rods a bit closer together, and thus the radius rod wasn't so far out of reach, or maybe it related more to differences in strength and thrust between the small and larger locos. The mid-sized gear was very similar to this smaller valve gear design, but the transfer of the combination rods to the valve chest was done via a moving transverse rod, rather than a long sliding link block. The first Mason locomotive to utilise this small valve gear design was the 1875 'Pegasus' for the Boston Revere Beach & Lynn RR. This was the first of the Mason 0-4-4T standard, and smaller than previous NG Mason Bogies. This was the first valve gear to use the guide cleat off the crosshead guide support bracket to restrain the end of the lifting rods off the bell rig, keeping them fixed in a vertical position, with a short link at the bottom end of the lifting rod to the radius rod. From Art Wallace's book, describing the motion of the Mason Valve gear on the 0-4-4T design: "The effect of this arrangement is expected to be nearly uniform distribution of steam to and from the cylinder.